In a conventional network, data is transferred between computers and peripherals to accomplish the data processing demands of the computers and peripherals. Demands for data to be transferred via the network may arise in any particular computer or peripheral in a manner unsynchronized with demands that arise on other computers and peripherals of the network. Data transfer to accomplish delivery is generally between respective ports of the computers and peripherals and may pass through switches having ports as well. Such switches have numerous ports and generally retransmit data (also called routing network traffic) from one port to another according to address information associated with the data to be transferred. A pair of ports communicate via a link between the ports.
Demands generally vary widely in the amount of data to be delivered over the network and the manner in which the delivery is to be made. For example, some demands may be made for a relatively large amount of data without regard to the order in which the data is delivered via the network. Other demands may require that the data be delivered in a particular order. Some demands may have no use for data that is presented outside of an expected time for delivery. Other demands may be met at any time, though system efficiency may suffer if delivery is made outside of an expected time for delivery.
With a large number of network links, use of the network may be regulated to some extent by establishing a priority for each link. In particular, when attempts to meet demands result in delivery of data in bursts between pairs of computers and/or peripherals, network performance may exhibit several undesirable results. Network capacity (sometimes colloquially referred to as bandwidth) for servicing lower priority links may be unavailable. Delivery of data may be noticeably delayed. More out of order deliveries may be made. And, service between ports on particular links may be denied intermittently, causing queues to fill and network capacity to be used for overhead messages regarding the control of network traffic as opposed to actually routing the traffic.
Traditional approaches to improving a network's ability to deliver data which would otherwise be delivered in bursts and to decreasing the likelihood of the undesirable results described above have focused on increasing network data transfer speed, increasing the depth of queues for data awaiting processing before or after transfer via the network, and increasing the instruction processing speed for processors (e.g., per-port processors) that accomplish delivery over the network. In a conventional architecture, each port may be implemented with a processor and memory dedicated to servicing all forms of traffic for that port.
In another known approach to solving some of the problems discussed above, a traffic stream having a traffic profile is affected by provisioning a facility for traffic conditioning as described in Request For Comment “An Architecture for Differentiated Services,” RFC2475 by S. Blake of Torrent Networking Technologies. A traffic profile is a set of desired temporal properties for a traffic stream (i.e., packet rate and burst size). A traffic stream is an administratively significant set of microflows that traverse a path segment as selected by a particular classifier. Provisioning includes mapping traffic streams to per hop behaviors, and specifying methods of traffic conditioning. Per hop behaviors are effected by shaping. Traffic conditioning is defined as classifying, metering, marking, shaping, and dropping packets. A microflow classifier selects packets (e.g., for marking) based on an arbitrary number of header fields including source address, destination address, protocol (e.g., IP), fields (e.g., DS field in IP header), source port, and destination port. Marking is defined (for IP) as setting the value of the DS field. Metering is defined as measuring temporal properties of a traffic stream. Shaping is delaying packets to conform a traffic stream to a desired traffic profile. Shaping includes enqueueing a marked packet and holding the packet in queue until transmitting the packet would not exceed a desired traffic profile. The basic architecture assumes that traffic conditioning functions are accomplished at each ingress and egress node (i.e., at each port of an edge node) of the network. According to a first conventional hardware architecture, all traffic conditioning functions would be accomplished by a central processing unit (CPU) serving a group of ports at an ingress and egress node. Such a CPU would not be capable of significant bandwidth. According to a second conventional hardware architecture, each port of an edge node would be implemented with a processor and memory dedicated to performing traffic conditioning functions by servicing all forms of traffic for that port.
A large portion of network traffic is associated with reading or writing data storage media. The data delivery problems described above are evident in networks that provide shared access to data storage devices. Managing data for improved access according to traditional approaches has included introducing servers between data storage devices and the network. Such server technology impedes network traffic flow, and may facilitate unexpected denial of access or damage to data due to failure mechanisms with a single point of failure.
Without the present invention, data delivery cannot be further improved without unreasonably increasing the cost per port of the network and the computers and peripherals that use the network. Increased costs stem from increased memory for queues and sophisticated processing instructions to be executed by the port processors, from increased processing speed, and from circuits that operate at higher frequencies to provide increased network data transfer speed. The comparatively high cost of circuits that operate at increased frequency stems from difficulties in designing such circuits and difficulties in fabrication.